“Floating screed” asphalt finishing machines, or pavers, have provided an efficient and economical method of coating an old or new roadway with a compacted layer of asphalt aggregate for many years. Floating screed pavers are generally known to those skilled in the art, as reflected by the disclosure contained in U.K. Patent 1,054,151 to the Blaw-Knox Company. Such a paver typically comprises a self-propelled traction unit, or tractor, having a hopper at its front end for receiving paving material, such as asphalt aggregate, from a dump truck. A conveyor system on the machine transfers the paving material from the hopper rearwardly for distribution in front of a floating screed. Transversely arranged screw augers positioned at the rear end of the traction unit assist in moving the paving material in a lateral direction with respect to the direction of movement of the paver, so that a relatively uniform volume of paving material is distributed across the portion of the roadbed in front of the floating screed.
The screed is commonly operated so as to “float” by virtue of being connected to the forwardly moving machine by means of pivoted leveling arms or tow arms. With forward movement, the screed physically levels any paving material lying higher than a predetermined height above the roadway surface, leaving a generally uniform thickness of such material. This function is enhanced by inclining the bottom surface of the screed so that its forward edge is higher than its rear edge, thereby providing a smaller area between the screed and the roadway and a large dragging surface at the rear of the screed. The angle defined between the bottom surface of the screed and the roadway surface is called the “angle of attack.” The screed also compacts the dragged paving material in order to provide a uniform, smooth, durable pavement surface. The screed is often mounted to vibrate against the pavement material to assist in spreading and compacting the material.
The leveling arms of the screed are attached to the paver traction unit at a “tow point.” In early pavers this point was a simple fixed pin connection. As a result, the thickness of the resulting paved mat could only be controlled by means of altering the screed angle of attack. Later paver designs allowed the tow point to be moved vertically using a tow point adjuster, causing a corresponding movement in the leveling arms and screed. This arrangement accommodated changes in the grade of the road surface by automatically fine tuning the initial setting of the screed angle of attack, thereby controlling the pavement mat thickness.
The screed has numerous controls that affect the temperature of the heater, the thickness of the mat, the shape of the edges, contours, etc. In an automatic mode, sensors are used to automatically adjust the screed for some or all of these settings. However, in a manual mode, an operator can control these aspects of the screed.
When in the manual state, there is no grade or slope automation system in use. Instead, an operator manually adjusts the tow point of the screed to create the desired mat profile. In order to have precise control, the tow point adjustment moves relatively slowly. That is, movement of the tow point operates at a fixed, slow rate either up or down to give the operator fine control of the mat profile. However, when creating an obstacle, such as a speed bump, or preparing the machine for transport, the fixed, slow speed can cause delays.
With respect to paving machine controls, U.S. Publication 2014/0186115 (the '115 publication) discloses linking different controls so that, for example, a change in screed height automatically increases auger height. The '115 publication fails to address problems related to the slow tow point adjustment speed in manual operation mode.